The present invention relates to a data transmission apparatus preferably applied to a video on-demand apparatus for sending data such as image data upon demand by audience.
In the video on-demand apparatus for providing programs as requested by audience, image data including movies and other various types of data are transmitted through a plurality of channels. One of the methods for implementing the video on-demand apparatus is to provide a magnetic-tape reproducing apparatus for each of a plurality of channels and send data for all the channels simultaneously or data for each channel one after another. Alternatively, using random access of such apparatuses as a hard disk unit and an optical disk unit, random access is performed on multiple types of data recorded on a single disk to send each type of data over each channel.
However, the method in which a magnetic-tape reproducing apparatus is provided on each channel increases the number of magnetic-tape reproducing apparatus, resulting in the costly video on-demand apparatus. Additionally, in this method, a magnetic tape is reproduced repetitively, imposing a hazard of damage thereof. Further, during time in which a magnetic tape is being rewound, the data transmission service is disabled. On the other hand, the method in which a random access disk apparatus is used requires to frequently repeat random access operations to send data for multiple channels. Consequently, if there are too many channels, the access time increases accordingly providing decreased time, and requiring to decrease the number of channels.